From New Scientist.com: "IT SOUNDS like an open-and-shut case: a clear DNA match is made between semen from a serious sexual assault and a blood sample from a known criminal. Yet in a recent case from Alaska, the criminal in question was in jail when the assault took place. And forensic scientists had already matched the crime sample to the DNA profile of another person who was their prime suspect. It was only after careful detective work that the mystery was solved: the jailed man had received bone marrow from the suspect many years earlier.

This week, at a meeting of the American Society of Human Genetics in Salt Lake City, Utah, Abirami Chidambaram of the Alaska State Scientific Crime Detection Laboratory in Anchorage described the case to highlight the danger of miscarriages of justice. Given the retribution that can be doled out to sex offenders by other jail inmates, the consequences could be severe. "If you implicate the wrong person, they can be killed in prison," says Chidambaram.

When Chidambaram discovered the perplexing match, she initially thought there had been a sample mix-up. But there was no mistake. What's more, the jailed man and suspect shared the same surname.Because medical records are confidential, a detective had to make further enquiries among family and friends of the two men. That revealed that not only were the convict and suspect brothers, but the inmate had received a bone marrow transplant from his brother. As a result, his blood was populated with cells bearing his brother's DNA profile.It's an instance of life imitating art: in November 2004, US TV channel NBC broadcast an episode of Law and Order: Special victims unit in which a rapist nearly got away with his crimes because of a similar bone-marrow mix-up." [Mark Godsey]